On board diagnostic systems are known from the automotive technology. These systems are vehicle diagnostic systems which monitor all emission-influencing systems during the operation and store possibly arising errors in a memory so that they may be queried and, if necessary, eliminated.
Common monitoring functions in the air system for internal combustion engines are in most cases configured in such a way that a characteristic (for example, system deviation) is determined from inputs (sensors, model values, . . . ) under certain release conditions used to establish an operating range. For this purpose, the air system must either be transferred into the established operating range or the monitoring functions must wait until the air system is transferred on its own into the established operating range. As soon as the air system is transferred into this established operating range, the characteristic is compared to the boundaries and an error is detected in the case of (permanent) exceedance of the boundaries.
Such common monitoring functions, however, monitor the air system only for their correct function and detect a malfunction per se. If a malfunction of the air system is determined, such common monitoring functions are presently not capable of qualifying this error. This makes the error diagnosis and the error cause investigation more difficult. Furthermore, it is possible that such common monitoring functions do not detect some of the errors at all. These are, in particular, those errors which do not result in any malfunctions of the internal combustion engine in the established operating range. This may be a soot clot, for example, which has settled in a valve and holds the valve open permanently. If the established operating range for the error diagnosis includes the valve in an open position, it is not possible to detect this error.
One possibility would be to monitor the air system over time. This is, however, complicated since a large amount of memory space is needed to store and evaluate the monitored signals. The evaluation itself is only marginally efficient since the air system greatly changes over time, resulting in errors being detectable only with great difficulties or not at all.